"Amidst the ethical turmoil of the denominations, voices are continually heard insisting that if we agree about Christ, other disagreements are not decisive. . . .
But "we cannot agree about Christ if we disagree about substantial matters of moral teaching. To suppose that we can implies serious misconceptions about Christ. . . . agreement about Christ cannot be only doctrinal. . . . the relationship between Jesus Christ and the law of God is such that we cannot agree in teaching about Christ if we disagree substantially about the law. . . .
"disputes about divine law involve, in the end, disputes about Jesus Christ, and therefore disputes about the gospel. . . ."
David Yeago, "Grace and the good life: why the God of the gospel cares how we live," in The morally divided body: ethical disagreement and the disunity of the church, ed. Michael Root and James J. Buckley, The Pro ecclesia series 1 (Eugene, OR: Cascade Books, 2012), 77-79 (77-92).
Many "claim that Christians have a unity 'in Christ' or 'in the gospel' that is somehow impervious even to very substantial disagreement about moral questions. I am speaking here not of the deep ontological unity founded by baptism, but about the concord in faith and teaching that is necessary for church-fellowship" (77).
"The knowledge of Jesus Christ is therefore not only what we might call doctrinal knowledge, but is inherently also knowledge of a way that Christians are summoned and privileged to walk, recognition of the good kind of life that we receive from Jesus Christ" (89-90).
Robert W. Jenson, in "Can ethical disagreement divide the church?" (Ibid., pp. 1-11):
"That matters of ethics have in fact divided the church, and that such divisions have in fact often been taken as holding at the same level as divisions caused by doctrine [(p. 2)], is a matter of open record. . . .
"For a more recent case, one may instance the Lutheran World Federation's break of fellowship with the white Lutheran churches of South Africa, on account of their practice of apartheid. The action was widely applauded at the time—including by some who now call for living together in spite of almost anything. The Lutheran churches trotted out the heavy artillery, status confessionis: tolerating apartheid was held to contradict the church's confession of faith" (p. 3).
That took place at the Sixth Assembly of the Lutheran World Federation in June of 1977. Cf. this, among others.
This is not the Lutheran document mentioned by Jenson, but it, too, insists that ethical disagreement can be church-dividing.